Advances in electronics has made electrical instruments more compact and more reliable than bulkier, older electrical instruments. Today, electrical instruments that perform a multitude of functions are portable and can be carried on the user's person or conveniently stored at home. Compactibility and reliability are especially important features for an electrical instrument that performs medical measurements, such as a reflectance photometer.
Persons with diabetes use reflectance photometers to monitor the sugar level in their blood. Compact and portable reflectance photometers can be carried by diabetics and allows them to periodically and conveniently monitor their blood.
Reflectance photometers determine the sugar values of a blood sample through color development. The user places a drop of blood onto a chemically treated strip. The strip changes color depending on the sugar concentration of the blood. The user then inserts the strip of paper into the reflectance photometer, and light from a light-emitting diode is reflected onto the colored strip. Reflected light passes through a wavelength filter and strikes a photodetector. The electrical signals from the photodetector are evaluated and the sugar concentration of the blood sample is determined and displayed by the reflectance photometer.
The reflectance photometer has different mode settings essential for providing reliable measurements. In a calibration mode, the reflectance photometer calibrates itself by emitting light from a light-emitting diode onto a white surface instead of the colored strip. In this way, the reflectance photometer compensates for any distortions on the reflector surface or minor defects that could cause incorrect readings. After calibration, a user inserts the chemically treated strip with blood into the reflectance photometer. The reflectance photometer analyzes the color of the strip and gives an accurate reading of the sugar level in the blood sample.
At present, several reflectance photometers use a rubber switch that is compressed by a compression lever to change operation mode. The lever is pivotally mounted at one end to the top cover of the reflectance photometer. When the cover is placed onto the reflectance photometer, the other end of the lever is engaging a cam slide, and the lever is positioned over the rubber switch. To calibrate the reflectance photometer, the user slides the cam slide that forces the lever to compress the rubber switch and engage with electrical contacts on the reflectance photometer's printed circuit board. To determine the sugar level in a blood sample, the user slides the cam slide in the opposite direction that forces the lever to disengage the rubber switch from the electrical contacts on the reflectance photometer's printed circuit board.
This arrangement between the switch and the lever presents a problem. The reflectance photometer manufacturer must install the rubber switch separately from the lever because the lever is mounted to the top cover. The rubber switch must be carefully placed in the proper position on the reflectance photometer's printed circuit board during the manufacture of the reflectance photometer. Many times, the rubber switch can fall off the printed circuit board or become misaligned with the lever, rendering mode switching impossible and the reflectance photometer useless. Even if the rubber switch remains properly positioned, the present rubber switch and lever configuration hampers the smooth operation of the reflectance photometer. The compression of the rubber switch causes a high degree of friction between the cam slide surface and the lever, and this friction prevents the smooth switching of the reflectance photometer into calibration mode.